A Model for Computational Science Investigations
AiS ChallengeSTI 2004
Richard Allen
Computational Science? Computational science seeks to gain an
understanding of science through the use of mathematical models on supercomputers.
Computational Science involves teamwork
Computational Science
Complements, but does not replace, theory and experimentation in scientific research.
Experiment
Computation
Theory
Computational Science
Is often used in place of experiments when experiments are too large, too expensive, too dangerous, or too time consuming.Can be useful in “what if” studies; e.g. to investigate the use of pathogens (viruses, bacteria, fungi) to control an insect population. Is a modern tool for scientific investigation.
Computational Science
Has emerged as a powerful, indispensable tool for studying a variety of problems in scientific research, product and process development, and manufacturing. • Seismology • Climate modeling • Economics• Environment• Material research
• Drug design• Manufacturing • Medicine • Biology
Analyze - Predict
Example: Industry
First jetliner to be digitally designed, "pre-assembled" on computer, eliminating need for costly, full-scale mockup.Computational modeling improved the quality of work and reduced changes, errors, and rework.
www.boeing.com/commercial/777family/index.html
Example: Roadmaps of the Human Brain
Cortical regions activated as a subject remembers the letters x and r.Real-time MRI techno-logy may soon be incor-porated into dedicated hardware bundled with MRI scanners allowing the use of MRI in drug evaluation, psychiatry, & neurosurgical planning. www.itrd.gov/pubs/blue00/hecc.h
tml
Example: Climate Modeling
3-D shaded relief representation of a portion of PA using color to show max daily temperatures.Displaying multiple data sets at once helps users quickly explore and analyze their data. www.itrd.gov/pubs/blue00/
hecc.html
Computational Science Process
Real World Problem
Identify Real-World Problem: Perform background research, focus
focus on a workable problem. Conduct investigations (Labs), if
if appropriate. Learn the use of a computational tool: C++,
Java, StarLogo, Excel, Stella, and Mathematica.Understand current activity and predict future
behavior.
Working Model
Simplify Working Model: Identify and select factors to describe important aspects of Real World Problem; deter- mine those factors that can be neglected. State simplifying assumptions. Determine governing principles, physical laws. Identify model variables and inter-relationships.
Mathematical Model Represent Mathematical
Model: Express the Working Model in mathematical terms; write down mathematical equations or an algorithm whose solution describes the Working Model.
In general, the success of a mathematical model depends on how easy it is to use and how accurately it predicts.
Computational Model Translate Computational
Model: Change Mathema- tical Model into a form suit- able for computational solu- tion.
Computational models include languages, such as C++ or Java, or software, such as StarLogo, Stella, Excel, or Mathematica.
Results/Conclusions Simulate Results/Con-
clusions: Run “Computational Model” to obtain Results; draw Conclusions. Verify your computer program; use check
cases; explore ranges of validity. Graphs, charts, and other visualization tools are
useful in summarizing results and drawing conclusions.
Real World Problem Interpret Conclusions:
Compare with Real World Problem behavior.
If model results do not “agree” with physical reality or experimental data, reexamine the Working Model (relax assumptions) and repeat modeling steps.
Often, the modeling process proceeds through several “cycles” until model is“acceptable”.
Computational Science Process
Computational Science Investigations
A Computational science investigation should include An application - a scientific problem of interest
and the components of that problem that we wish to study and/or include.
Algorithm - the numerical/mathematical repre-sentation of that problem, including any numerical methods or recipes used to solve the algorithm.
Architecture – a computing platform and software tool(s) used to compute a solution set for the algorithm.
Example: A Falling Rock
Determine the motion of a rock dropped from a height H, above the ground with initial
velocity V.
Working Model
Governing principles: d = v*t and v = a*t.Simplifying assumptions:
Gravity is the only force acting on the body. Flat earth. No drag (air resistance). Model variables are H,V, g; t, s, and v.
Working Model (cont.)
Form a discrete-in-time model to determine the position and velocity of the rock above the ground at equally spaced times, t0, t1, t2, …, tn; e.g. t0 = 0 sec, t1 = 1 sec; t2 = 2 sec, etc.
v0 v1 v2 … vn
s0 s1 s2 … sn
|______|______|____________|_____ t0 t1 t2 … tn
100
90
80
70
60
50
40
30
20s = D
ispl
acem
ent (
in m
eter
s)
2
0
0
0
Initial conditions
9.8 / sec , 1.0 sec100 , 10.0 / sec
Problem variables:0
10010.0
g m tH m V m
ts Hv V
10
0
0 1 2 3 4t = time (in seconds)
An Illustration
An Illustration (cont.)
100
90
80
70
60
50
40
30
20s = D
ispl
acem
ent (
in m
eter
s)
0
0
0
0100
10.0
tsv
10
0
0 1 2 3 4t = time (in seconds)
1 0
1 0
1 0 1
1
1 0 1
0 1.0 1.0* 10.0
90.0* 9.8
19.8
t t ts v t
s s sv g t
v v v
An Illustration (cont.)
100
90
80
70
60
50
40
30
20s = D
ispl
acem
ent (
in m
eter
s)
1
1
1
190.0
19.8
tsv
10
0
0 1 2 3 4t = time (in seconds)
2 1
2 1 1
2 1
1.0 1.0 2.0* 70.2* 29.6
t t ts s v tv v g t
An Illustration (cont.)
100
90
80
70
60
50
40
30
20s = D
ispl
acem
ent (
in m
eter
s)
2
2
2
2.070.2
29.6
tsv
10
0
0 1 2 3 4t = time (in seconds)
3 2
3 2 2
3 2
2.0 1.0 3.0* 40.6* 39.4
t t ts s v tv v g t
An Illustration (cont.)
100
90
80
70
60
50
40
30
20s = D
ispl
acem
ent (
in m
eter
s)
3
3
3 340.6
39.4sv
t
10
0
0 1 2 3 4t = time (in seconds)
4 3
4 3 3
4 3
2.0 1.0 4.0* 1.2* 49.2
t t ts s v tv v g t
Mathmatical Model
Given an initial time, t0, an initial height, H, and an initial velocity, V, generate the time history of heights, sn, and velocities, v, by the formulas
0 0
1 1
1
,,,
1, 2,
n n n n n
n n n n
s H v Vs v t s s sv g t v v v
n
Computational Model
Pseudo CodeInput
t0, initial time; V, initial velocity; H, initial heightg, acceleration due to gravity; Δt, time step;imax, maximum number of steps
Outputti, t-value at time step isi, height at time tivi, velocity at time ti
Example: Falling Rock
Initializeset ti = t0 = 0; vi = v0 = V; si = s0 = Hprint ti, si, vi
Time stepping: i = 1, imaxset ti = ti + Δtset si = si + vi*Δtset vi = vi - g*Δtprint ti, si, viif (si <= 0), quit Excel Model
Interpretation
To create a more more realistic model of a falling rock, some of the simplifying assumptions could be dropped; e.g., incor-porate drag - depends on shape of the rock, is proportional to velocity. Improve discrete model: Approximate velocities in the midpoint of time
intervals instead of the beginning. Reduce the size of Δt.
A Virtual Science Laboratory
The site below is a virtual library to visualize science. It has projects in mechanics, electricity and magnetism, life sciences, waves, astrophysics, and optics. It can be used to motivate the development of mathematical models for computational science projects.
explorelearning
Referenced URLs
AiS Challenge Archive site www.challenge.nm.org/Archive/
Explorescience sitewww.explorelearning.com
Boeing examplewww.boeing.com/commercial/777family/index.html
Road maps for the human brain and climate modeling exampleswww.itrd.gov/pubs/blue00/hecc.html
An interesting modeling site
Formulating modelswww.cnr.colostate.edu/class_info/nr575/webfiles/
L05_Formulating_Continuous_Time_Models.pdf Falling bodies
http://hypertextbook.com/physics/mechanics/falling/
Master tools http://www.shodor.org/master/